To your first problem: In the simple agricultural example, clearing the land has a reasonably predictable cost, whether it is taking down centuries-old trees and removing stumps and roots, or removing the boulders, or removing the spring harvest of rocks that surface due to winter freezes and placing them onto walls. Often the soil must be drained, and fenced, and possibly irrigated. But not all the land will be improved at once; uncleared land will be close to cleared, fenced, drained land, and obviously a tenant or buyer will pay more for partially improved farmland than for unimproved.
To your second problem: Where in the US is there unowned land? The settlers went west across thousands of miles of unoccupied land. Why didn't they stop and settle? It was owned. Early and ultimate sprawl. Others had pre-empted it for the benefit of their heirs. Think how the development of the US would have been had development proceeded west in some orderly way.
To your third problem: the land is forever. If well taken care of, it will remain fertile. But its fertility may not be important for all that long, depending on its location; its highest and best use will stop being agriculture. Buildings built for one purpose gradually deteriorate, and as the community changes, are no longer suitable to the current highest and best use of that land. At one time in NYC - say, 1880 - 21 year leases were common, and huge department stores and other edifices were built on them. It was understood that another building would likely follow. And it did. And the landlord got his "share." How did he earn that share? And look at the teardowns in your part of the country. Homes that seem perfectly serviceable to some of us are bought to be torn down to build something else on that well-located land. It doesn't happen on the edge of town; it happens in the center of things. The price one is willing to pay to get that land is pretty clear: the transaction plus the cost of removing the old improvement.
To your fourth problem: the land owner who doesn't improve his land can still sell it for a higher price due to the activity of the community around him. The value of the improvements never exceeds their replacement value, but could be quite a bit less. A huge spa resort built 15 or 20 miles from Disney World is likely an over-development of the land it is built on, while closer to DW, it might be quite appropriate and profitable. One who is building with consideration to others' preferences -- as customers or as tenants -- will build differently from one who simply wants what they want, without regard to resale value. We don't increase the unimproved value of our own sites, but we can contribute to the value of the surrounding sites -- or we might decrease the value. Increasing it doesn't exempt us from any portion of the value of our own site. Our neighbors' actions can increase or decrease the value of our own site. Regular reassessments take that into account.
To your second problem: Where in the US is there unowned land? The settlers went west across thousands of miles of unoccupied land. Why didn't they stop and settle? It was owned. Early and ultimate sprawl. Others had pre-empted it for the benefit of their heirs. Think how the development of the US would have been had development proceeded west in some orderly way.
To your third problem: the land is forever. If well taken care of, it will remain fertile. But its fertility may not be important for all that long, depending on its location; its highest and best use will stop being agriculture. Buildings built for one purpose gradually deteriorate, and as the community changes, are no longer suitable to the current highest and best use of that land. At one time in NYC - say, 1880 - 21 year leases were common, and huge department stores and other edifices were built on them. It was understood that another building would likely follow. And it did. And the landlord got his "share." How did he earn that share? And look at the teardowns in your part of the country. Homes that seem perfectly serviceable to some of us are bought to be torn down to build something else on that well-located land. It doesn't happen on the edge of town; it happens in the center of things. The price one is willing to pay to get that land is pretty clear: the transaction plus the cost of removing the old improvement.
To your fourth problem: the land owner who doesn't improve his land can still sell it for a higher price due to the activity of the community around him. The value of the improvements never exceeds their replacement value, but could be quite a bit less. A huge spa resort built 15 or 20 miles from Disney World is likely an over-development of the land it is built on, while closer to DW, it might be quite appropriate and profitable. One who is building with consideration to others' preferences -- as customers or as tenants -- will build differently from one who simply wants what they want, without regard to resale value. We don't increase the unimproved value of our own sites, but we can contribute to the value of the surrounding sites -- or we might decrease the value. Increasing it doesn't exempt us from any portion of the value of our own site. Our neighbors' actions can increase or decrease the value of our own site. Regular reassessments take that into account.